The present invention relates generally to image reproducing systems, and more particularly relates to electrostatic latent image formation and development systems for providing a transferable image.
A typical electrostatographic printing process includes a development step whereby developing material including toner or marking particles is physically transported into the vicinity of a latent image bearing imaging member, with the toner or marking particles being caused to migrate via electrical attraction of toner or marking particles to the image areas of the latent image so as to selectively adhere to the imaging member in an image-wise configuration.
Various methods of developing a latent image have been described in the art of electrophotographic printing and copying systems. Of particular interest with respect to the present invention is the concept of forming a thin layer of liquid developing material on a first surface, wherein the layer has a high concentration of charged marking particles. The layer is brought into contact with an electrostatic latent image on another surface, wherein development of the latent image occurs upon separation of the first and second surfaces, as a function of the electric field strength generated by the latent image. In this process, toner particle migration or electrophoresis is replaced by direct surface-to-surface transfer of a toner layer induced by image-wise fields. The developed image is typically formed on an image bearing member for subsequent transfer and fusing (transfusing) to a receiver substrate. In such printing methods, the image quality can vary significantly due to numerous conditions affecting such transfusing.
Embodiments of the present invention provide an improvement in performing contact electrostatic printing, and particularly for performing direct transfer of a developed image, formed on an image bearing member operable in a contact electrostatic printing system, to a wide range of receiver substrates.
Methods and apparatus for transferring and fusing a developed toner image from an image bearing member to a receiver substrate in a Contact Electrostatic Printing (CEP) system are provided according to the present invention. The developed toner image is formed of a development material, preferably having a mixture of carrier fluid and pigmented polymeric particles, the composition of such material being selected for its characteristic behavior at an elevated temperature for transitioning to a substantially single phase.
A method of contact electrostatic printing according to the present invention includes the steps of developing an image onto an image bearing member, the developed image being formed of the aforementioned development material; concentrating the developed image by processing the developed image so as to increase its solids content; heating the concentrated developed image to a temperature at which the mixture of pigmented polymeric particles and the carrier fluid achieve a substantially single phase; and transferring the concentrated developed image, now in a substantially single phase condition, to a receiver substrate such as a paper sheet.
A method of contact electrostatic printing according to the present invention includes the steps of: forming a uniform layer of liquid development material; charging the liquid development material layer to a first polarity; transforming the uniform layer to a toner cake layer by removing an upper portion of the layer via squeegee roll or self-gap reverse metering device, with appropriate bias applied to prevent developer material offset, to form a toner cake layer; transferring the toner cake layer to a photoreceptor having thereon an electrostatic latent image; reversing the toner cake layer charge in an image-wise fashion; separating the toner cake layer into a developed image and a background image, the developed image being developed onto a compliant image bearer; processing the toner cake layer in the developed image by increasing the solid content of the developed image to a high solids content level, e.g. in the range of 35 to 80%, by use of a fluid regulating device; heating the toner cake layer in the processed image to an elevated temperature above the phase-mixing temperature boundary of the toner cake to cause a transition to a substantially single-phase condition, thus forming a transferable image; and transferring the transferable image from the compliant image bearer to the receiver substrate.
An embodiment of the present invention includes apparatus for forming an image in a toner cake layer in accordance with a reverse charge contact electrostatic printing system (CEP), wherein the apparatus includes a first subsystem for forming the image and a second subsystem for developing the image to a compliant image bearer, and for concentrating and heating the toner cake layer as described above to provide a transferable image, with subsequent transfer of the transferable image. The compliant image bearer advantageously allows for transfer of the transferable image to a wide range of substrates.
An improved processed color image can be attained in embodiments of the present invention that employ a tandem or image-on-image (IOI) printing system architecture. No intermediate transfer belt is required in such printing systems.
The developer material preferably includes carrier liquid and pigmented polymeric or optionally non-pigmented polymeric particles, which form a substantially single phase at elevated temperatures. Pigment material in the toner particle is typically insoluble in toner resin or carrier fluid. In the description of the invention herein, the described single phase behavior is assumed to exclude typical pigments, and referring more specifically to the characteristic of a toner resin to form a substantially singe phase with a carrier fluid.
The present invention provides for an imaging system that employs a fluid regulating device to adjust the fluid content of a toner cake in order to prepare the toner cake for transition to the single phase condition. Such an imaging system includes a toner, cake applicator for applying toner cake onto a receiving member, a charging devil disposed so as to form an electrostatic latent image in the toner cake, a separation subsystem positioned relative to the receiving member so as to selectively separate at least a portion of the imaged toner cake from the receiving member, and a fluid regulating device for regulating the amount of fluid in the toner cake. For example, the fluid regulating device may be adapted to increase the concentration of toner particles in the toner cake by adjusting the amount of carrier fluid.
According to another aspect, the imaging system of the present invention further includes an imaging device positioned so as to apply an electrostatic latent image onto the receiving member prior to the application of the toner cake. The imaging device can include an image exposure station.
According to another aspect, the separation subsystem is adapted to receive at least a portion of the toner cake from the receiving member and for transferring at least a portion of the toner cake to a compliant substrate. The separation subsystem includes a compliant image bearing member for receiving a portion of the toner cake from the receiving member.